The subject of this article does not contribute canonical content to the BattleTech universe, either because it is not intended to or because it is not an official product.See the article's section on Canonicity for details.

An ongoing project, the Faction Assignment & Rarity Tables, originally known as the 3028 Random Mech Assignments & Appendix and also often called the Xotl RAT tables and by many similar names, is a freely available fan-made BattleTech resource authored chiefly by Keith "Xotl" Hann. The titular timeframe was changed at some point to "3028-3050", although by now tables are in fact provided for timeframes as early as 2750 (the Star League era) and tables for beyond 3050 are being worked on.

Provided for download (here) as a free PDF document, the Faction Assignment & Rarity Tables are highly detailed Random Assignment Tables (RATs) for BattleMechs and vehicles in (primarily) the late Succession Wars era, with ongoing work to produce tables for other eras. In addition, the document provides a faction availability listing, a Quirks rundown, and other secondary information.

Since its first publication via the BattleTech Forum, the document has constantly been checked, updated and improved with input from a broad range other contributors. Being the result of meticulous research, it is generally held in high esteem among the BattleTech fan base as the ultimate, and most accurate, set of RATs. Whereas RATs in various official sourcebooks are invariably inaccurate because of the limitations of the 2d6 roll resolution they have to be based on, and also because of being concerned with balancing for the scenario at hand over "historical" accuracy, Hann's Faction Assignment & Rarity Tables are concerned with availability only, irrespective of gameplay issues, and are d1000-based which allows for a much finer representation of relative commonness.

Being entirely fan-made, the document itself is not canonical. However, it can be considered to be a meta-source because it collates canonical production data, with educated guesswork filling in for some blanks.